Platelet tests in the prediction of myocardial infarction and ischaemic stroke: evidence from the Caerphilly Prospective Study

A platelet test that is predictive of myocardial infarction (MI) and/or str oke would enable the targeting of anti-platelet drugs towards high-risk pat ients. The predictive power of several platelet tests for MI and for stroke was examined in 2000 older men in the Caerphilly Cohort Study of Heart Dis ease, Stroke and Cognitive Decline. The tests were: aggregation to adenosin e diphosphate (ADP) in platelet-rich plasma (PRP): aggregation to ADP in wh ole brood measured using an impedance method and a test of platelet aggrega tion induced in whole blood by high-shear flow Around 200 MIs and 100 ischa emic strokes occurred during a 10-year follow-up. Neither primary nor secon dary aggregation in PRP was predictive of MI. However the fifth of men in w hom the primary response to ADP was least, showed the highest risk of a sub sequent stroke [relative odds (RO) 1.64; 95% confidence interval (CI) 1.12- 2.43]. Aggregation in whole blood was not predictive of MI but, again, the fifth of men with the least platelet response showed the highest stroke inc idence (RO 1.79; 95% CI 1.06-3.00). Retention of platelets in the high-shea r test was not predictive of either event.